Method of making printing-forms with fine screen for stereotype-work.



UNITED STATES PATENT OFFICE.

ROBERT WILI-IELM MAX NITZSCHE, 0F OBEROARSDORF, GERMANY.

METHOD OF MAKINGv PRINTING-FORMS WITH FINE SCREEN FOR STEREOTYPE-WORK.

No Drawing.

To all whom it may concern:

Be it known that I, ROBERT WILHELM max NrrzscI-IE, residing at Obercarsdorf, in the kingdom of Saxony, German Empire, have invented certain new and useful Improvements in Methods of Makin Printing- Forms with Fine Screen for tereotypelVork, of which the following is a specification.

The reason why stereotype casts of screened printing forms, in particular half tone blocks with fine screen. have not been heretofore obtained in a satisfactory manner, lies in the fact that the impressed matrix boards which, as known, are obtained by couching several layers of but little sized paper pulp onto each other, will naturally have a coarse and rough surface, which in consequence of the unavoidable imprint of the felt will have an uneven and irregular surface. These irregularities of the surface are caused by an irregular distribution of the pulp, or, in other words, an irregular density at the various points, so that when the block is impressed onto such board, it will meet, at different points, a different resistance and a different degree of compression. By such denser and less dense parts lying next to each other of various expanse, the reprint of the surfaces which, in the block have an even tone, will become cloudy. Some, closely limited denser parts will even result in local defects in the print. It is obvious that in impressing the block not only the irregularities of the outer surface but also such of the lower layers will come into efiect.

This fact alone proves that a coating of the one side only, the upper side, with a paste of chalk or baryta will not afford a perfect remedy. But such a coating even has the disadvantage, that when the block is impressed, particles of such coating will be cracked ofi" or will be locked in the fine recesses of the screened surface and be torn off when the block is removed, so that defective spots are caused in the stereotype form, and the block is soiled for a later impression. Only by an extremely careful preparation and dressing of the matrix board by expensive, tedious and careful manual labor it was possible to obtain by the said method casts which gave satisfaction.

Calandering the boards would be quite unsuitable, as this would impair the impressibility of the board. But even if this were not the case, the irregularities would be re- Specification of Letters Patent.

Application filed December 22, 1916.

Patented Nov. 6, 1917.

Serial No. 138,524.

moved outwardly only, or, in other words, be driven inward, so that the density of the board and in consequence thereof its impressibility would be varied at different points. For the same reasons it is of no avail to cover a soft pasteboard core with a smooth calandered paper covering.

Neither has the adoption of the Foudrinier machine brought any success, which machine turns out endless pasteboard webs and by the cooperation of the wire cloth with heated drying rolls, with smooth surfaces thereon, because the impressibility of the matrix boards produced by such'method is too small and the smoothness of the product is likewise an outward one only.

It has now been possible to satisfactorily solve the problem by grinding the matrix boards manufactured in the usual manner, subsequently on both sides. By thus removing the superfluous material a smooth surface and at the same time the necessary uniformity in thickness and density is obtained; this latter so much easier and surely, as the grinding means (the grains of the grinding medium) will, at the denser points, find a ess, it might be possible to substitute rapidly revolving steel edges for the grinding medium, at least for the rough-grinding process.

Although the present method originated in the intention to find a satisfactory stereotyping process for screened printing forms, it may also be employed with matrix boards which are intended for common stereotype purposes, such as stereotyping letterpress and wood blocks (engravings)-and will, in such cases, render good services particularly in printing fine or delicate fonts or engravings.

I claim:

1. The art of producing stereotype matrix boards which consists in subjecting matrix boards composed of couched layers of lightly sized paper pulp to a surface grinding in different directions substantially as herein set forth.

The art of producing stereotype matrix boards which consists in subjecting matrix boards composed of couched layers of lightly sized paper pulp to a surface, grinding in different directions in successive stages of rough grinding finishing and polishing substantially as herein set forth.

8. A matrix board for stereotype casts consisting of a multiplex sheet composed of united couchedlayers.ofpulp'having a regular thickness and a polished ground surface. 15

In testimony whereof- 1 affix my signature in presence of two witnesses.

ROBERT WILHELM MAX NITZSCHE.

Witnesses:

MARTA PI EL, BERT. BRAINE.

Copies of thisp atent gnay be obtained f orfive cents eac h by addressing the Qornmis s iouer of Iatents, Washington D. C. 

